Metrology tool error log analysis methodology and system

ABSTRACT

A method of identifying failures in a metrology tool system used to measure desired dimensions in microelectronic features. Each metrology tool in the system runs a plurality of recipes for measuring desired dimensions in microelectronic features, with each recipe comprising a set of instructions for measuring at least one dimension in a microelectronic feature. The system includes an error log having stored thereon failures in measurement of microelectronic feature dimensions. The method includes determining normalized number of errors for the recipes used by the metrology tool from the failures stored in the error log, identifying one or more recipes having the greatest normalized number of errors in the error log, identifying, in a list of jobs to be performed by the metrology tool, the one or more identified recipes having the greatest normalized number of errors, and from the identified one or more recipes having the greatest normalized number of errors, determining the cause of the errors in the one or more recipes. The method then includes effecting a change in the one or more identified recipes having the greatest normalized number of errors to correct the errors therein and tracking a metrology tool job having the one or more recipes in which a change has been effected to determine whether the cause of errors has been corrected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the manufacture of semiconductordevices and, in particular, to the identification of failures in ametrology tool used to measure dimensions in microelectronic features.

2. Description of Related Art

During microelectronics manufacturing, a semiconductor wafer isprocessed through a series of tools that perform lithographic processingto form features and devices that form the microelectronic circuits andother features on the substrate of the wafer. Lithographic systemsreplicate circuit patterns by projecting the image of a mask patternonto a wafer, and consist of imaging tools that expose patterns andprocessing tools that coat, bake and develop the substrates. The patternmay consist of features of varying size and density, all of which mustbe printed simultaneously with dimensional fidelity to design. As usedherein, the term critical dimension (CD) or critical width refers to thesmallest dimension of a pattern or feature that can be produced by thelithographic system. Such processing has a broad range of industrialapplications, including the manufacture of semiconductors, flat-paneldisplays, micromachines, and disk heads.

Generally after each process step, any errors on the wafer are measuredand controlled using metrology tools that image dimensions either onportions of the microelectronic circuits themselves or on specializedtargets printed on the wafer. Such circuit portions, targets, and otherfeatures shall be generally referred to as microelectronic features,unless otherwise specified. The metrology tools use so-called recipes tomake measurements of desired microelectronic features. Such recipesgenerally comprise maps of the microelectronic features and commands tothe tools optical measurement systems to align the particular feature tobe measured with the tool measurement device, by rotation andtranslation of the wafer with respect to the tool, and to use therequired tool measurement device. A typical tool measurement device mayuse purely optical schemes to obtain the respective measurements,examples of these types of tools include overlay, scatterometry and filmthickness. Other tool measurement devices include an optical device inconjunction with a scanning electron, atomic force microscopy or someother combination where each tool measurement device is designed tomeasure specific process steps along the way during chip fabrication.From this point forward measuring a desired dimension of amicroelectronic feature can mean measuring critical dimensions, overlay,film thickness, depth and the like.

As metrology tools become more and more advanced, they require moreskill on the part of the user. The experience needed to createmeasurement recipes is quickly becoming out of the reach of the averageuser. Additionally, the number of process steps being measured onmetrology tools is growing with each new generation chip process. For 65nm node chip technology, the chip may pass through a critical dimension(CD) metrology tool about 70 times in the course of its processing. Eachof those 70 passes requires a unique recipe to be constructed. Manytimes dozens of different types of chips are being created using the 65nm node chip technology, with each of the same process steps for eachunique chip requiring a unique metrology recipe. Such CD metrologyrecipes can easily number in the thousands.

Knowing that a high level of expertise is needed to create a robustrecipe, many chip fabricators do not have sufficient manpower to allowall of these thousands of recipes to be created as robustly as needed.In many cases the recipes created do not run robustly. Over time thisbecomes a significant issue that directly affects the cycle time neededto build a fully functioning chip; in some extreme cases it affectsyield. Since it could take a year or more to master programming recipeson some metrology tools, poorly written metrology recipes create majorproblems in metrology tool management, cycle time and process debug.

With the thousands of recipes that exist on metrology tools used tomonitor the processes in making chips, there is a need for effective wayof determining which recipes are most problematic. Further, there aremany opportunities for a production lot at a particular process step tofail using the metrology recipe created to monitor that process step.Given that a chip fabricator may have a dozen or more CD tools measuringall the different chips at different process steps during theirlifetime, coupled with many poorly written recipes, the amount of recipefailures could reach levels in the tens of thousands within a fairlyshort time period. A recipe failure may pause the metrology tool,resulting in a lot that did not measure robustly to go on hold andrequire investigation. This and other situations can, in turn, slow downthe chip construction and directly impact the cycle time. Without aneffective way of determining the problematic recipe, much time andresources may be wasted.

SUMMARY OF THE INVENTION

Bearing in mind the problems and deficiencies of the prior art, it istherefore an object of the present invention to provide a method ofidentifying, from numerous metrology tool recipe failures, the mostproblematic recipes that need to be fixed.

It is another object of the present invention to provide a method ofdetermining where to begin the process of fixing metrology tool recipesthat have failed.

A further object of the invention is to provide an automated method ofconverging on the most problematic metrology tool recipes and determineroot cause.

It is yet another object of the present invention to provide a method ofidentifying and repairing metrology tool recipe failures using errorlogs that exist on metrology tools.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The above and other objects, which will be apparent to those skilled inthe art, are achieved in the present invention which is directed to amethod of identifying failures in a metrology tool used to measuredesired dimensions in microelectronic features comprising providing ametrology tool running a plurality of recipes for measuring desireddimensions in microelectronic features, each recipe comprising a set ofinstructions for measuring at least one dimension in a microelectronicfeature, and providing an error log for the metrology tool, the errorlog having stored thereon failures in measurement of microelectronicfeature dimensions. The method includes determining normalized number oferrors for the recipes used by the metrology tool from the failuresstored in the error log, identifying one or more recipes having thegreatest normalized number of errors in the error log, identifying, in alist of jobs to be performed by the metrology tool, the one or moreidentified recipes having the greatest normalized number of errors, andfrom the identified one or more recipes having the greatest normalizednumber of errors, determining the cause of the errors in the one or morerecipes. The method then includes effecting a change in the one or moreidentified recipes having the greatest normalized number of errors tocorrect the errors therein and tracking a metrology tool job having theone or more recipes in which a change has been effected to determinewhether the cause of errors has been corrected.

Prior to identifying the recipes having the greatest normalized numberof errors, the method preferably includes determining whether the errorsare caused by a recipe used by the metrology tool, and using only theerrors caused by a recipe to identify the one or more recipes having thegreatest normalized number of errors and determine the cause of theerrors therein. If the errors are not caused by a recipe used by themetrology tool, the method may include repairing the metrology toolhaving the failure not caused by a recipe.

There may be provided a plurality of the metrology tools, with each toolhaving a plurality of recipes, and the error log has stored thereonfailures in measurement of microelectronic feature dimensions for theplurality of metrology tools. The method may include identifying commonrecipes having errors in a plurality of the metrology tools, anddetermining the cause of the errors in such common recipes.

The metrology tool failures stored in the error log may includealignment errors, pattern recognition errors and dimensional measurementerrors, hardware failures and software failures, including instances ofrebooting. The method may further include summarizing failures stored inthe error log, and storing summarized failure data in a database.

In another aspect, the present invention is directed to a computerprogram product comprising a computer useable medium including acomputer readable program for identifying failures in a metrology toolsystem used to measure desired dimensions in microelectronic features,wherein the metrology tool system includes a metrology tool adapted torun a plurality of recipes for measuring desired dimensions inmicroelectronic features, with each recipe comprising a set ofinstructions for measuring at least one dimension in a microelectronicfeature. The metrology tool has an error log in a database having storedthereon failures in measurement of microelectronic feature dimensions.The computer readable program when executed on the computer causes thecomputer to determine normalized number of errors for the recipes usedby the metrology tool, from the failures stored in the error log,identify one or more recipes having the greatest normalized number oferrors in the error log, and identify, in a list of jobs to be performedby the metrology tool, the one or more identified recipes having thegreatest normalized number of errors.

The computer readable program when executed on the computer furthercauses the computer to summarize failures stored in the error log, andstore summarized failure data in a database.

Where the metrology tool system includes a plurality of the metrologytools, each tool has a plurality of recipes, and the error log hasstored thereon failures in measurement of microelectronic featuredimensions for the plurality of metrology tools. In such case, the oneor more recipes having the greatest normalized number of errors may beidentified for the metrology tools. The computer readable program whenexecuted on the computer may further cause the computer to summarizefailures stored in the error log, and store summarized failure data in adatabase.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel and the elementscharacteristic of the invention are set forth with particularity in theappended claims. The figures are for illustration purposes only and arenot drawn to scale. The invention itself, however, both as toorganization and method of operation, may best be understood byreference to the detailed description which follows taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a schematic of the metrology tool system capable of practicingthe method of the present invention.

FIG. 2 is a flowchart showing the preferred general method ofidentifying failures in a metrology tool used to measure desireddimensions in microelectronic features, in accordance with the presentinvention.

FIG. 3 is a flowchart showing the preferred method of identifyingspecific problem areas in one or more metrology tools in a metrologytool system.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In describing the preferred embodiment of the present invention,reference will be made herein to FIGS. 1–3 of the drawings in which likenumerals refer to like features of the invention.

The method of identifying failures in a metrology tool used to measuredesired dimensions in microelectronic features described herein permitsthe user to quickly converge on the most problematic recipes anddetermine root cause using the error logs that typically exists on eachand every metrology tool. This process can be automated, and when runperiodically, gives the user the information needed to begin addressingthe worst-performing recipes with solutions, thereby causing the failurerate to decrease over time.

As described above, metrology tools may encounter failures during thecourse of running a recipe to make microelectronic feature measurement,and a metrology tool error log records every recipe and tool failureover time. If such an error log does not exist on an existing tool, onemay be established by one skilled in this art. The information or datain the error log may be accessed or sent to a database and processedusing the methodology described below. As also described above, eachrecipe has numerous parts to it that could fail when measuring a givenprocess step. A typical CD recipe may have the following categoriescaptured as failures in the error log: Optic GA (global alignment);Optic PR (pattern recognition); SEM (scanning electron microscope) GA;SEM PR; Measurement; Manual Measurement; and Others.

The Optic GA and Optic PR errors may occur while the metrology recipe isdetermining how to calculate and remove the wafer-loading rotation errorusing pattern recognition prior to making measurements using an opticalmicroscope. Next, using the CD SEM metrology tool, the opticalmicroscope is switched to the electron microscope where a highermagnification global alignment can be used to make even finercorrections to any loading errors in the wafer. Once all optical and SEMGA activities have finished, the measurements of the microelectronicfeatures may begin. Each process parameter being measured (criticaldimension in the case of the CD SEM) typically has a pattern recognitionstep (SEM PR) and then a feature measurement (Measurement) is made. Thisprocess is repeated many times over the wafer until all requiredmicroelectronic feature measurements are made. Any (or all) of theaforementioned steps may fail. Another type of error occurs when anautomatic measurement cannot be made and a manual measurement is invoked(Manual Measurement). There may be other recipe failure types that canbe categorized under the Other category.

The metrology tool system may comprise a single metrology tool or aplurality of metrology tools connected by a network, such as a localarea network (LAN) or even the Internet. As shown in FIG. 1, metrologytool system 20 comprises metrology tools 24 a, 24 b, 24 c connected bynetwork 32 to controller 26, which contains microprocessor 28 and hasaccess to database 30. Tools 24 a, 24 b, 24 c run individual recipesfrom database 30, as directed by the microprocessor of controller 26, tomake measurements of one or more dimensions of microelectronic featureson wafers 22 a, 22 b, 22 c, respectively. Recipe and non-recipe failuresencountered by the metrology tools in making the microelectronic featuremeasurements are stored in an error log database 30.

In practicing the preferred method of the present invention, each of therecipe failure categories can be summarized for a given recipe that hasrun many times over a period of time. This summary guides the user todetermine what to repair in the recipe as identified as having a highdegree of failure. Other categories of information may be summarized ina metrology tool error log.

The preferred method 100 of identifying failures in a metrology toolsystem used to measure desired dimensions in microelectronic features isshown in FIG. 2. The method begins with the raw error log information102 stored on a database associated with the metrology tool system oranother database to which the data was previously downloaded, such asdatabase 30 (FIG. 1). The data information is then accessed, and summarystatistics are calculated 104 for each recipe for a given time period.If a plurality of metrology tools is networked in the system, as in theexample here, fleet-wide statistics are calculated for all of the tools.Examples of such statistics are total number of failures, number ofwafers run, number of failures per wafer, average time it took eachwafer to run, 3 sigma of wafer run times, range of wafer run times, andthe like. Many of these statistics can be used as diagnostics forfurther diagnosis of cycle time issues. Preferably, these summarizedstatistics are sent 110 to the database for historical analysispurposes, which can be used to determine and verify whether recipesfixed over time remain fixed.

The recipes are sorted 106 for given time period by those with mosterrors per wafers run or by other normalized standard to determine whichrecipes failed most. The most problematic recipes are identified 108 andverified to be actual recipe issues before being addressed. This steprules out that a particular tool or tools caused the majority offailures because there were tool issues, and rules out whether somewafers that had the majority of errors were deviated engineering wafersusing a process of record (POR) metrology recipe.

If recipe issues did not cause the failures, the other issues areinstead addressed 112. This eliminates wasting time fixing the recipe,if some other issues would explain the failures. If recipe issues causedthe failures, the recipe is added 114 to a list of recipes that have themost normalized failures and need fixing, i.e., the so-called heavyhitter list. In this step one may also analyze the failed recipe bycategorizing how many failures were received per the type of categorydiscussed above.

Once the recipes that need repair are identified, the next job cominginto a metrology tool using this recipe is identified and the recipetherein is placed on hold to be fixed 116. The particular part of therecipe(s) that needs to be fixed is also noted. Subsequently, theidentified recipe(s) that need repair are then analyzed to determine thecause of errors, and a change is effected and the errors are corrected118. The analysis and repair may also be made prior to identifying thelist of jobs to be run with the recipe(s) needing repair. The metrologytool jobs using the recipe are then tracked to determine whether thecause of errors has been corrected.

The method of identifying and repairing metrology tool recipes returnsto step 104 and keeps iterating to generate a list of a number n ofrecipes that have the most normalized errors, e.g., a top 10 list, for agiven time period. The method is revisited consistently over time toreduce the recipes that are most problematic.

In parallel with the method of addressing recipe failures of FIG. 2, themethod of the present invention also provides a method 120 ofidentifying non-recipe based metrology tool failures or alarminformation regarding-specific tool problems such as reboots, hardwareor software failures, and the like, as shown in FIG. 3. Initially, theraw error log information for such non-recipe based metrology toolfailures is input from the database 122, i.e., that information that isstored on a database associated with the metrology tool system oranother database to which the data was previously downloaded. After thedata information is accessed, summary statistics are then calculated 124for each non-recipe tool failure. The unique tool alarms are categorizedand counted over given time periods, by tool, and fleet-wide statisticsare calculated for the tools in the system. Summarized data is sent to adatabase 126 to track tool performance over time with respect tonon-recipe based metrology tool failures 126. The non-recipe basedmetrology tool failures are then studied and solved, preferably on thepriority of the tools with most problems over a given time period.

The present invention can take the form of an entirely hardwareembodiment, e.g., the database of the metrology tool system, an entirelysoftware embodiment or an embodiment containing both hardware andsoftware elements. In a preferred embodiment, the method of the presentinvention described above is implemented in software, which includes butis not limited to firmware, resident software, microcode, or othercomputer usable program code.

Furthermore, the invention can take the form of a computer programproduct accessible from a computer-usable or computer-readable mediumproviding program code, such as database 30, for use by or in connectionwith a computer or any instruction execution system, such as controller26 and microprocessor 28, as shown in FIG. 1. For the purposes of thisdescription, a computer-usable or computer-readable medium can be anyapparatus that can contain, store, communicate, propagate, or transportthe program for use by or in connection with the instruction executionsystem, apparatus, or device. The medium can be an electronic, magnetic,optical, electromagnetic, infrared or semiconductor system (or apparatusor device) or a propagation medium. Examples of computer-readable mediuminclude a semiconductor or solid state memory, magnetic tape, aremovable computer diskette, a random access memory (RAM), a read-onlymemory (ROM), a rigid magnetic disk and an optical disk. Currentexamples of optical disks include compact disk—read only memory(CD-ROM), compact disk—read/write (CD-R/W) and DVD.

A data processing system suitable for storing and/or executing programcode will include at least one processor, such as microprocessor 28,coupled directly or indirectly to memory elements through a system bus.The memory elements can include local memory employed during actualexecution of the program code, bulk storage, and cache memories whichprovide temporary storage of at least some program code in order toreduce the number of times code must be retrieved from bulk storageduring execution.

Input/Output or I/O devices of the metrology tools and system controller(including but not limited to keyboards, displays, pointing devices,etc.) can be coupled to the system either directly or throughintervening I/O controllers.

Network adapters may also be coupled to the system network 32 to enablethe data processing system to become coupled to other data processingsystems or remote printers or storage devices through interveningprivate or public networks. Modems, cable modem and Ethernet cards arejust a few of the currently available types of network adapters.Preferably, the program embodying the method of the present inventionpermits remote analysis of tool error logs, allows analysis ofpreviously downloaded tool error logs, and connects to the database oferror logs to allow probing of historical data regarding recipe andnon-recipe based metrology tool failures. In the analysis of tool errorlogs, the error log data may be downloaded to a remote computer 34 forimmediate or future analysis.

The analysis of tool error logs can provide lists of total tool systemerrors and identification of recipes having the most normalized errors,as well as a summary of errors for each individual tool in the systemalong with information on each wafer lot run by that tool, e.g.,chronological ordering of lots, respective number of errors, and theprocessing time. The analysis may also provide identification of errorsby category, e.g., Optic GA, Optic PR, SEM GA, and the like, to providedirection for which recipes and problems should be addressed first.Analysis of wafer lots also provides information on whether productionor engineering jobs were responsible for the majority of recipefailures. Non-recipe based tool failures may also be analyzed in thismanner.

Thus, the present invention provides a method of identifying the mostproblematic recipes that need to be fixed from analysis of numerousmetrology tool recipe failures, as well as a method of determining whereto begin the process of fixing metrology tool recipes that have failed.The invention provides an automated method of converging on the mostproblematic metrology tool recipes and determining root cause, andidentifying and repairing metrology tool recipe failures, using errorlogs that exist on current metrology tools.

While the present invention has been particularly described, inconjunction with a specific preferred embodiment, it is evident thatmany alternatives, modifications and variations will be apparent tothose skilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives, modifications and variations as falling within the truescope and spirit of the present invention.

1. A method of identifying failures in a metrology tool used to measuredesired dimensions in microelectronic features comprising: providing ametrology tool running a plurality of recipes for measuring desireddimensions in microelectronic features, each recipe comprising a set ofinstructions for measuring at least one dimension in a microelectronicfeature; providing an error log for the metrology tool, the error loghaving stored thereon failures in measurement of microelectronic featuredimensions; from the failures stored in the error log, determiningnormalized number of errors for the recipes used by the metrology tool;identifying one or more recipes having the greatest normalized number oferrors in the error log; identifying, in a list of jobs to be performedby the metrology tool, the one or more identified recipes having thegreatest normalized number of errors; from the identified one or morerecipes having the greatest normalized number of errors, determining acause of the errors in the one or more recipes; effecting a change inthe one or more identified recipes having the greatest normalized numberof errors to correct the errors therein; and tracking a metrology tooljob having the one or more recipes in which a change has been effectedto determine whether the cause of errors has been corrected.
 2. Themethod of claim 1 further including, prior to identifying the recipeshaving the greatest normalized number of errors, determining whether theerrors are caused by a recipe used by the metrology tool, and using onlythe errors caused by a recipe to identify the one or more recipes havingthe greatest normalized number of errors and determine the cause of theerrors therein.
 3. The method of claim 1 further including summarizingfailures stored in the error log, and storing summarized failure data ina database.
 4. The method of claim 1 wherein there is provided aplurality of the metrology tools, each having a plurality of recipes,wherein the error log has stored thereon failures in measurement ofmicroelectronic feature dimensions for the plurality of metrology tools,and wherein the one or more recipes having the greatest normalizednumber of errors is identified, and the cause of the errors therein isdetermined for each metrology tool.
 5. The method of claim 1 whereinthere is provided a plurality of the metrology tools, each having aplurality of recipes, wherein the error log has stored thereon failuresin measurement of microelectronic feature dimensions for the pluralityof metrology tools, and including identifying common recipes havingerrors in a plurality of the metrology tools, and determining the causeof the errors in such common recipes.
 6. The method of claim 1 whereinthe metrology tool failures stored in the error log include failuresselected from a group consisting of hardware failures and softwarefailures, including instances of rebooting.
 7. The method of claim 6further including summarizing failures stored in the error log, andstoring summarized failure data in a database.
 8. The method of claim 1further including, prior to identifying the recipes having the greatestnormalized number of errors, determining whether the errors are causedby a recipe used by the metrology tool and, if the errors are not causedby a recipe used by the metrology tool, repairing the metrology toolhaving the failure not caused by a recipe.
 9. A method of identifyingfailures in a metrology tool system used to measure desired dimensionsin microelectronic features comprising: providing a metrology toolsystem having a plurality of metrology tools, each tool running aplurality of recipes for measuring desired dimensions in microelectronicfeatures, each recipe comprising a set of instructions for measuring atleast one dimension in a microelectronic feature; providing an error logfor the metrology tool system, the error log having stored thereonfailures in measurement of microelectronic feature dimensions for eachmetrology tool; determining whether errors are caused by a recipe usedby a metrology tool in the system; from the failures stored in the errorlog caused by a recipe, determining normalized number of errors for therecipes used by the metrology tool system; identifying one or morerecipes having the greatest normalized number of errors in the errorlog; identifying, in a list of jobs to be performed by the metrologytool system, the one or more identified recipes having the greatestnormalized number of errors; from the identified one or more recipeshaving the greatest normalized number of errors, determining a cause ofthe errors in the one or more recipes; effecting a change in the one ormore identified recipes having the greatest normalized number of errorsto correct the errors therein; and tracking a metrology tool job havingthe one or more recipes in which a change has been effected to determinewhether the cause of errors has been corrected.
 10. The method of claim9 further including summarizing failures stored in the error log, andstoring summarized failure data in a database.
 11. The method of claim 9wherein the metrology tool failures stored in the error log includefailures selected from a group consisting of alignment errors, patternrecognition errors and dimensional measurement errors.
 12. The method ofclaim 9 including identifying common recipes having errors in aplurality of the metrology tools in the system, and determining thecause of the errors in such common recipes.
 13. The method of claim 9wherein the metrology tool failures stored in the error log includefailures selected from a group consisting of hardware failures andsoftware failures, including instances of rebooting.
 14. The method ofclaim 13 further including summarizing failures stored in the error log,and storing summarized failure data in a database.
 15. The method ofclaim 9 wherein, if the errors are not caused by a recipe used by themetrology tool system, further including repairing the metrology toolhaving the failure not caused by a recipe.
 16. A computer programproduct comprising a computer useable medium including a computerreadable program for identifying failures in a metrology tool systemused to measure desired dimensions in microelectronic features, themetrology tool system including a metrology tool adapted to run aplurality of recipes for measuring desired dimensions in microelectronicfeatures, each recipe comprising a set of instructions for measuring atleast one dimension in a microelectronic feature, the metrology toolhaving an error log in a database having stored thereon failures inmeasurement of microelectronic feature dimensions, wherein the computerreadable program when executed on a computer causes the computer to:determine normalized number of errors for the recipes used by themetrology tool, from the failures stored in the error log; identify oneor more recipes having the greatest normalized number of errors in theerror log; and identify, in a list of jobs to be performed by themetrology tool, the one or more identified recipes having the greatestnormalized number of errors.
 17. The computer program product of claim16 wherein the computer readable program when executed on the computerfurther causes the computer to summarize failures stored in the errorlog, and store summarized failure data in a database.
 18. The computerprogram product of claim 16 wherein the metrology tool system includes aplurality of the metrology tools, each having a plurality of recipes,wherein the error log has stored thereon failures in measurement ofmicroelectronic feature dimensions for the plurality of metrology tools,and wherein the one or more recipes having the greatest normalizednumber of errors is identified for the metrology tools.
 19. The computerprogram product of claim 16 wherein the metrology tool failures storedin the error log include failures selected from the group consisting ofhardware failures and software failures, including instances ofrebooting.
 20. The computer program product of claim 19 wherein thecomputer readable program when executed on the computer further causesthe computer to summarize failures stored in the error log, and storesummarized failure data in a database.